1. Field of the Invention
The present invention relates to a film scanner, and more particularly, to a film scanner with an adjustable light source whose chromaticity can be adjusted according to the film to be scanned.
2. Description of the Prior Art
As film scanners have assumed an increasingly important role in graphic image processing, users have realized the importance of scanners with high image quality, demanding both image clarity and true color representation. Obviously, the color character of scanned films is an important consideration when choosing parts affecting the color output of a film scanner.
In general, there are two types of films used in film scanners: positive films and negative films. Please refer to FIG.1 and FIG. 2. FIG. 1 shows a transmitted spectrum generated by fully exposed positive films. FIG. 2 shows a transmitted spectrum generated by unexposed negative films. As can be seen from FIG. 1 and FIG. 2, the ratio of the spectrum distribution of transmitted rate (or absorption rate) for positive films is vastly differently from that of negative films, i.e., the transmitted rate R.sub.650 :G.sub.540 :B.sub.450 of exposed positive films under a standard light is about 1:1:1, and that of unexposed negative films is about 4.0:1.3:1.0. This indicates that there is an even transmitted rate for red, green, and blue colors on positive films but a significantly higher transmitted rate for red on negative films. Therefore, under the same illuminating conditions and duration, positive films will display balanced chromaticity while negative films will display an unbalanced chromaticity with a higher brightness of red.
To overcome the problem of the difference of transmitted rate between positive and negative films, most film scanners are provided with a color scanner module having shutter function. The shutter function adjusts the exposure time for red, green, and blue colors creating balanced chromaticity of scanned images. Unfortunately, the shutter function makes color scanning modules costly, takes more exposure time, and thus slows down scanning speed.